This invention relates to a driving device (a linear actuator) and, in; particular, to a driving device where an electro-mechanical transducer such a piezoelectric element is used as a driving source of the driving device (the linear actuator).
Previously, linear actuators (driving devices) using electro-mechanical transducers such as piezoelectric elements, electrostrictive elements, magnetostrictive elements, or the like are used as auto-focus actuators or zoom actuators for use in cameras.
By way of illustration, Japanese Patent No. 2633066 (JP-B 2633066) (which will be also called a first patent document), which corresponds to U.S. Pat. No. 5,225,941, discloses a driving device comprising a driving rod frictionally engaged with a lens barrel, a piezoelectric element disposed in contact with the driving rod, and a leaf spring for bringing the driving rod into frictional engagement with the lens barrel. That is, the driving rod is bonded to an end of the piezoelectric element in an expansion direction. The lens barrel is movably supported to the driving rod. The leaf spring produces friction between the driving rod and the lens barrel. In the driving device disclosed in JP-B 2633066, a voltage is applied to the piezoelectric element so as to make a speed of expansion of the piezoelectric element different from a speed of contraction thereof.
In addition, Japanese Patent No. 3218851 (JP-B 3218851) (which will be also called a second patent document), which corresponds to U.S. Pat. No. 5,589,723, discloses a driving apparatus comprising a piezoelectric element, a driving member (a driving shaft), coupled to the piezoelectric element, for extending in an expansion direction of the piezoelectric element, and a driven member (a moving member, a lens barrel) having a friction member frictionally coupled to the driving member (the driving shaft). The driving apparatus in JP-B 3218851 drives the lens barrel by devising a driving signal applied to the piezoelectric element. Japanese Patent No. 3180557 (JP-B 3180557) (which will be also called a third patent document), which corresponds also to U.S. Pat. No. 5,589,723, discloses a driving apparatus including the friction member composed of a metal and the driving member made of a fiber-reinforced resin composite.
Japanese Unexamined Patent Application Publication No. 2006-54979 (JP-A 2006-54979) (which will be also called a fourth patent document) discloses an actuator which is capable of moving a driven member with stability and with precision. The actuator disclosed in JP-A 2006-54979 comprises a first piezoelectric element, a diving member mounted to the first piezoelectric element, a driven member which is frictionally coupled to the driving member and which extends in a driving direction, and a second piezoelectric element for engaging the driving member with the driven member and for releasing a friction engagement between the driving member and the driven member. Specifically, the actuator disclosed in JP-A 2006-54979 comprises a pair of first piezoelectric elements for driving, a second piezoelectric element for engagement, a pair of driving members, and a pressure spring. The pair of first piezoelectric elements and the pair of driving members are disposed at both sides with the driven member sandwiched between them. The pair of driving members have a distance which is expanded or narrowed by the second piezoelectric element. By the second piezoelectric element, the friction engagement between the pair of the driving members and the driven member is ensured or released.
Japanese Unexamined Patent Application Publication No. H9-191665 (JP-A 9-191665) (which will be also called a fifth patent document), which corresponds to U.S. Pat. No. 5,890,391, discloses a linear drive mechanism using an electromechanical conversion element which is insensitive to elastic deformation of a constituent member. The linear driving mechanism disclosed in JP-A 9-191665 comprises the electromechanical conversion element, a working member which is fixedly connected to the electromechanical conversion element and which displaces with the electromechanical conversion element, a driving member frictionally coupled to the working member, a driven member coupled to the driving member, and a driving pulse generating arrangement for causing expansion/contraction displacement to the electromechanical conversion element.
Japanese Unexamined Patent Application Publication No. 2006-5998 (JP-A 2006-5998) (which will be also called a sixth patent document) discloses a liner actuator in which optimum surface roughness is specifically defined in a contact state of a frictionally coupled portion between a transfer member (a vibration friction portion) for transferring vibration of a piezoelectric element and a moving member (a moving portion) which is frictionally coupled to the transfer member (the vibration friction portion). In JP-A 2006-5998, a rod made of carbon is used as the transfer member and a combination of a metal slider and a cap which sandwich the rod is used as the moving member.
Japanese Unexamined Patent Application Publication No. H10-337057 (JP-A 10-337057) (which will be also called a seventh patent document), which corresponds to U.S. Pat. No. 6,188,161, discloses a driving apparatus capable of high speed driving in a high frequency range. In the driving apparatus disclosed in JP-A 10-337057, a movable member is movably supported by a fixed shaft (a driving shaft). Aligned in the direction of the fixed shaft, a piezoelectric element has one expansion end which is connected to one end of the movable member. The piezoelectric element has another expansion end which is connected to a driving friction member. The driving friction member comprises a main body that is connected to the piezoelectric element and a pair of semi-cylindrical protrusions that protrude toward the fixed shaft from a side of the main body. The pair of protrusions elastically grasp the fixed shaft from both above and below, and are in friction contact with the fixed shaft. The driving friction member is made lightweight, highly elastic, highly movable and very hard by using an aluminum alloy treated with anode oxide coating. JP-A 10-337057 neither discloses nor teaches a material of the fixed shaft (the driving shaft).
Japanese Unexamined Patent Application Publication No. H7-49442 (JP-A 7-49442) (which will be also called an eighth patent document) discloses a driving device comprising a driving member vibrating in an axial direction and a driven member making friction contact with the driving member. In the driving device disclosed in JP-A 7-49442, the driving member and the driven member are formed from frictional anisotropic materials in which the frictional coefficient between the driving member and the driven member is differed in positive and reversed vibrating direction of the driving member.
Furthermore, Japanese Patent No. 3171000 (JP-B 3171000) (which will be also called a ninth patent document), which corresponds also to U.S. Pat. No. 5,589,723, discloses a driving apparatus which is capable of realizing high speed movement. The driving apparatus disclosed in JP-B 3171000 comprises a support member (a stationary member), an electro-mechanical transducer, a driving member (a vibration friction portion), a barrel (a moving member), and a friction adding member (a plate spring). The electro-mechanical transducer has an end in an expansion/contraction direction that is fixed to the stationary member. The electro-mechanical transducer is applied with a voltage so that the electro-mechanical transducer expands and contracts at different speeds on expanding and on contracting, respectively. The driving member (the vibration friction portion) is connected to another end of the electro-mechanical transducer and is supported so as to move in the expansion/contraction direction of the electro-mechanical transducer. The moving member is frictionally engaged with the driving member and is supported so as to move in the expansion/contraction direction of the electro-mechanical transducer. The friction adding member provides a friction force between the driving member and the moving member. The driving member and the moving member are set to generate sliding therebetween even when the electro-mechanical transducer is expanded and contacted. However, JP-B 3171000 neither discloses nor teaches specific materials of the driving member (the vibration friction member) and the moving member.
There are problems in the above-mentioned first through forth patent documents as follows.
In the driving device disclosed in the first patent document, inasmuch as the lens holder (the driven member, the moving portion) is movably supported to the guide bar (the driving member, the vibration friction portion) bonded to the piezoelectric element, the guide bar (the driving member, the vibration friction portion) has a length longer than that of the lens holder (the driven member, the moving portion) and the guide bar (the driving member, the vibration portion) is easy to produce an inclination caused by a reciprocating motion. In addition, the longer a moving distance of the lens holder (the driven member, the moving portion), the longer the guide bar (the driving member, the vibration friction member) and it results in easily producing an unnecessary vibration mode. Furthermore, inasmuch as the friction engagement portion lies on an extension of a coupling portion between the piezoelectric element and the guide bar (the driving member, the vibration friction member), it counts against a reduction in profile thereof.
In also the driving apparatus disclosed in the second patent document, inasmuch as the driving shaft (the driving member, the vibration friction portion) extends in an expansion/contraction direction of the electro-mechanical transducer, the driving shaft (the driving member, the vibration friction portion) has a length longer than that of the a zoom lens barrel (the driven member, the moving portion) and the driving shaft (the driving member, the vibration friction portion) is easy to produce an inclination caused by a reciprocating motion. In addition, the longer a moving distance of the zoom lens barrel (the driven member, the moving portion), the longer the driving shaft (the driving member, the vibration friction portion) and it results in easily producing an unnecessary vibration mode. Furthermore, inasmuch as the friction engagement portion lies on an extension of a coupling portion between the electro-mechanical transducer and the driving shaft (the driving member, the vibration friction member), it counts against a reduction in profile thereof. In addition, inasmuch as the driving apparatus has structure where the zoom lens barrel (the driven member, the moving portion) is cantilevered by the driving shaft (the driving member, the vibration friction portion), it is impossible to mechanically move a large weight object such as the lens.
The third patent document may just disclose the driving apparatus where the driving shaft (the driving member, the vibration friction portion) is made of the fiber-reinforced resin composite and has a basic structure which is similar to that illustrated in the second patent document. It has therefore disadvantage which is similar to that of the second patent document.
Although the driving member (the vibration friction portion) has a length which is shorter than that of the driven member (the moving portion) in the actuator disclosed in the fourth patent document, the actuator disclosed in the fourth patent document is disadvantageous in that it is complicated in structure and it is impossible to reduce a size thereof because it comprises a plurality of piezoelectric elements.
On the other hand, the fifth patent document discloses the linear drive mechanism where the moving member (the moving portion) has a rod shape and the working member (a vibration friction portion) has a complicated shape. Incidentally, in order to improve moving efficiency of the moving portion due to vibration displacements of the vibration friction portion that are generated by the electro-mechanical transducer, it is necessary to adjust a coefficient of kinetic friction and a coefficient of static friction between the vibration friction portion and the moving portion to optimum values or conditions. For this purpose, it is necessary to select suitable materials for the vibration friction portion and the moving portion. However, the fifth patent document neither discloses nor teaches the materials of the vibration friction portion and the moving portion.
The sixth patent document defines the surface roughness of the vibration friction portion and the moving portion which are frictionally coupled to each other. However, in the manner which is described above, in order to improve the moving efficiency of the moving portion due to vibration displacements of the vibration friction portion generated by the electro-mechanical transducer, it is necessary to adjust the coefficient of kinetic friction and the coefficient of static friction between the vibration friction portion and the moving portion to optimum values or conditions. The coefficient of kinetic friction and the coefficient of static friction have values which change dependent not only on the surface roughness of the vibration friction portion and the moving portion but also on the hardness and density of materials of both.
Although the seventh patent document may describe the material of the driving friction member, but the seventh patent document neither discloses nor teaches the material of the fixed shaft (the driving shaft). The eighth patent document merely discloses the driving device comprising the driving member and the driven member which are formed from frictional anisotropic materials. The ninth patent document neither discloses nor teaches specific materials of the driving member (the vibration friction member) and the moving member.
At any rate, although it is necessary for the driving device to transfer vibrations generated by the electro-mechanical transducer to the vibration friction portion with a high degree of efficiency, any of the first through the neigh patent documents neither discloses nor teaches the materials of the vibration friction portion and the moving portion which are suitable to realize this.